1. Field of the Invention
The present invention generally relates to a high speed inspection system for manufacturing processes and, more particularly, to an inspection system capable of assuring the integrity of precision manufactured products. The invention has particular application to the inspection of parts, such as printed circuit boards (PCBs) or cards and the like.
2. Description of the Prior Art
The architectures of inspection machines fundamentally are separated into three categories: design rule types, reference based types and a combination of design rule and reference based types.
The design rule type operates on the converted optical image alone making measurements according to the rules of design of the part being inspected. Such design rules include minimum conductor line and space widths and are applied within the context of the inspection image.
The reference based type operates on both the converted optical image and some form of a stored ideal image. It is necessary to have both images in registration for the operation. The reference image either is compared with the inspection image or controls the processing of it.
Real-time processing of images requires sufficient processing power in the form of hardware that is distributed such that the images are simply operated on upon arrival at the first stage and the partial image results are passed on to the next stage of processing. The amount of image processing accomplished is dependent upon the pipeline length of the cascaded processing stages.
An image processor can be described as non-pipeline if the same processor operates successively upon the original and resulting images to completion. Such processors include two-dimensional array processors, parallel sets of one-dimensional image microprocessors and relatively simple template matching and measurement operations.
One type of reference based inspection system processes the image to form a list of discovered features. Those features may be a segment of a conductor, a conductor end, a conductor bend, etc. The reference image may be similarly processed to form a similar list. The two lists are then compared. There are two forms of feature generation and comparison. The first is the kind where the reference image is registered with the image and the features of both images are compared immediately upon generation. The second is the kind where the reference image is once converted into features and those features are registered and compared each time with the inspection features generated from the image.
Template matching describes a type of operation in reference based and design rule systems. In the design rule system, a fixed two-dimensional template is used to measure the minimum feature size, such as a conductor. Additional processing of the results are required to render the defect. In reference based processing, the template can be a fixed minimum size template, such as a conductor bend, invoked by the reference image to be compared with the image. It could also be a direct comparison with a minimum form of the reference image.
Morphological processing involves successive modifications of inspection and reference images for the purpose of extracting significant topological information. It is more involved than template matching in that a multiple of image transformations are required in order to extract the information. Yet, the extents of image solutions are limited only by the creativity of the morphological processing designer or programmer.